Unfair pricing

I took my car in on a Thursday got a quotation, I then paid for it to be done on the next day. The next day was a Friday i brought it in, I was later called to be told that it won't be done that Friday because they can't find the right parts as I was there for brakes, I then fetched it and was told to bring it on Saturday. I got there very early in the morning before they opened just to be told my car needed also a disc and that the money I paid is just a deposit because the disc of my car is hard to get and expensive, I then left with the car and brought it back on Monday, it was then done, I was again asked to pay now a lot more money which when I queried the price after a guy who was there for the same car model and same fault told me his price. The answer was that I had to pay two times for labour because mine was the brakes and the disc so they charge separately per job for those two.